Heat-resistant aluminum hydroxide and method for preparation thereof

ABSTRACT

A heat-resistant aluminum hydroxide which is prepared by subjecting a mixture of aluminum hydroxide with a reaction retardant for retarding the conversion aluminum hydroxide to boehmite, as a raw material, to the hydrothermal treatment or to pressurization and heating in a steam atmosphere; and a method for preparing a heat-resistant aluminum hydroxide which comprises subjecting a mixture of aluminum hydroxide with a reaction retardant for retarding the conversion aluminum hydroxide to boehmite as a raw material to the hydrothermal treatment, or to pressurization and heating in a steam atmosphere.

FIELD OF THE INVENTION

The present invention relates to a new aluminum hydroxide having ahigher dehydration temperature and a sufficiently large amount ofdehydration water, in particular to a new aluminum hydroxide favorableas a flame retardant for synthetic resins, and a method of producing thesame

BACKGROUND OF THE INVENTION

Synthetic resins have been used widely in various areas, and a flameretardant is generally added to flammable resins for providing flameresistance. In particular, currently when the use amount of aself-extinguishing flame-resistant resin polyvinyl chloride is decliningbecause of its adverse effects on environment, the use amounts offlammable resins such as polyethylene, polypropylene, and polystyreneare increasing as the replacement, which, in turn, is leading toincreased demand for flame retardants. In addition, a flame retardant isoccasionally added even to flame-resistant synthetic resins forimprovement in flame resistance.

Thus, various flame retardants have been provided. The flame retardantsused include phosphorus-based retardants (Japanese Patent ApplicationLaid-Open (JP-A) No. 2002-80633), halogen-based retardants (JP-A No.8-291128), inorganic hydrates such as aluminum hydroxide (JP-A No.2002-338816), magnesium hydroxide (JP-A No. 2003-3171), and boehmite(JP-A No. 2002-2091); and the like. However, phosphorus-based flameretardants have an environmental problem, for example, of causingaquatic eutrophication, while halogen-based flame retardants ofgenerating smoke and hazardous gases during combustion or incineration,which are attracting attention recently as a possible cause of seriousfire deaths, and thus, there exists a need for inorganic flameretardants having no such drawbacks. Among inorganic flame retardants,particularly aluminum hydroxide (Al(OH)₃) is rich in constitutionalwater, superior in flame-retarding effect and in acid and alkaliresistances, and also advantageous from the point of cost, and thus arewidely used. As for the flame-retarding properties of aluminumhydroxide, dehydration is known to start gradually at approximately 200°C. and progress rapidly at around 230° C. to 250° C.

However, many thermoplastic resins have a molding temperature at aroundthe dehydration temperature of aluminum hydroxide, and dehydration ofaluminum hydroxide during molding often resulted in drop in yieldbecause of the bubbles generated in the synthetic resin molded productsand the irregularity on the surface thereof. Although thermosettingresins are often molded at a temperature lower than that ofthermoplastic resins, these resins are occasionally used at a highertemperature because of the inherent properties of the synthetic resins,for example, as the parts in electric/electronic devices, and aluminumhydroxide therein occasionally resulted in dehydration depending on theenvironment temperature used, leading to decrease in the yield anddeterioration in the physical properties of molded products. For examplewhen a thermosetting resin is used as an electronic board, theenvironment temperature of the electronic board reaches as high asapproximately 230° C. during soldering, leading to dehydration ofaluminum hydroxide and consequently to decrease in the yield of theelectronic board.

Under the circumstances, it would be possible to use other inorganicflame retardants having a higher dehydration temperature. However, forexample, boehmite (AlO(OH)), which has a dehydration peak of around 500°C., may seem advantageous, but has a drawback of containing a smalleramount of constitutional water. Alternatively, magnesium hydroxide(Mg(OH)₂), which has a high dehydration peak temperature of about 380°C., is strongly alkaline, facilitating decomposition of the syntheticresin, and unstable to acids, and thus had problems, for example, ofprohibiting use thereof in an environment for example in contact withacid and easier solubilization thereof during etching of electronicdevice parts with acid. Magnesium hydroxide also had a drawback in thatit is converted to its basic carbonate salt under high-humiditycondition by absorption of the carbon dioxide gas in air, causing awhitening phenomenon of the resin surface containing the flame retardantmagnesium hydroxide and affecting the properties of the product.

Accordingly, an aluminum hydroxide flame retardant having a higherdehydration temperature and a sufficiently large amount of dehydrationwater is most desirable.

SUMMARY OF THE INVENTION

Objects of the present invention is to provide an aluminum hydroxidesuperior in flame-retarding properties that has a higher dehydrationtemperature, generates a smaller amount of foam due to dehydration atthe environment temperature of molding or using synthetic resins, doesnot cause drop in the yield of synthetic resin products, and contains asufficient amount of dehydration water, and a method of producing thesame.

The heat-resistant aluminum hydroxide according to the presentinvention, which achieves the objects above, can be produced by treatinga mixture of aluminum hydroxide and a reaction retarder underhydrothermal condition or by applying pressure and heat thereto under asteam atmosphere. The heat-resistant aluminum hydroxide is aluminumhydroxide that retains a sufficient amount of water for dehydration andhas a heightened dehydration temperature even after hydrothermaltreatment at a temperature in high temperature range or application ofpressure and heat under a steam atmosphere because of reduced conversionto boehmite. The hydrothermal treatment means heat treatment of amixture of aluminum hydroxide and a reaction retarder in a pressurevessel such as autoclave, in the presence of water in an amountsufficient to make the vessel saturated with steam (hereinafter,referred to as wet treatment). Alternatively, the treatment byapplication of pressure and heat under a steam atmosphere means apressurization treatment of a mixture of aluminum hydroxide and areaction retarder in a pressure vessel such as autoclave, in the absenceof water or in the presence of water in an amount smaller than thatneeded for saturating the vessel with steam (hereinafter, referred to asdry treatment). The heat-resistant aluminum hydroxide according to thepresent invention can be produced by heating the raw materials, aluminumhydroxide and a reaction retarder for retarding boehmite conversion,without addition of water in a pressure vessel heat. The processing byheating raw materials without addition of water in a pressure vesselmeans a treatment of raw materials under heat without addition of waterto the raw materials while generating no steam except the steam from thewater dehydrated from some of the aluminum hydroxide as raw material(hereinafter, referred to as dry treatment). Alternatively, the rawmaterials may be pressurized not only by the pressure by steam but alsoby supplying compressed air into the pressure vessel from outside.

The reaction retarder is a substance that delays conversion of aluminumhydroxide to boehmite in the wet or dry treatment and provides analuminum hydroxide that has no or low boehmite conversion rate evenafter a severe heat history (a high processing temperature and a longprocessing period allowing conversion of all aluminum hydroxide toboehmite). Generally in wet or dry treatment, almost all aluminumhydroxide is converted to boehmite even after a relatively mild heathistory (normally, 160° C./3 hours in dry treatment, 170° C./10 hours inwet treatment (water/aluminum hydroxide: 3 by weight), and 170° C./3hours in wet treatment (water/aluminum hydroxide: 3 by weight) in thepresence of added sodium hydroxide (sodium hydroxide/aluminum hydroxide:1/12, by molar ratio)). However, by using the reaction retarderaccording to the present invention, it is possible to reduce theboehmite conversion rate of aluminum hydroxide sufficiently and heightenthe dehydration temperature markedly even after a severe heat history,for example, in a wet or dry treatment at 215° C. for 10 hours.

The mechanisms for the rise of the dehydration temperature seem to be(1) reinforcement of the Al—O bonds in aluminum hydroxide crystal byrearrangement caused by the severe heat history, and (2) increase in thesurface smoothness of aluminum hydroxide and reduction in the number ofdehydration-starting points due to solubilization of a trace amount ofaluminum hydroxide by the severe heat history (dehydration seems to beinitiated at the surface cracks (defects) on aluminum hydroxide and leadto development in the size of the cracks, which in turn leads to furtherdehydration in chain reaction).

The processing temperature in the wet or dry treatment is 170° C. ormore and 300° C. or less, and preferably 200° C. or more and 250° C. orless. It is because a lower processing temperature prohibits sufficientrise of the dehydration temperature, and although a higher processingtemperature is favorable as the heat history is enhanced, an excessivelyhigh temperature often raises the boehmite conversion rate, demandingincrease in the amount of the reaction retarder added for suppressingthe reaction and resulting in drastic increase of the pressure duringtreatment, making it unpractical to use an autoclave. The processingperiod in the wet or dry treatment is 1 hour or more and 24 hours orless, and preferably 5 hours or more and 10 hours or less. It is becauseit is difficult to raise the dehydration temperature sufficiently in ashorter processing period, and although a longer processing period isfavorable as the heat history is enhanced, an excessively elongatedperiod often raises the boehmite conversion rate, demanding increase inthe amount of the reaction retarder added for suppressing the reaction.

The reaction retarder is not particularly limited, if it is in accordwith the above-mentioned definition, and examples thereof includeinorganic acids or the salts thereof such as sulfuric acid, nitric acid,phosphoric acid, tetrafluoroboric acid, ammonium dihydrogen phosphate,sodium dihydrogen bisphosphate monohydrate, sodium dihydrogen phosphate,and potassium metaphosphate; organic acids or the salts thereof such asacetic acid, succinic acid, lactic acid, fumaric acid, and tartaricacid; silicon compounds and fluorine compounds such as silica,silane-coupling agent, white carbon, hexafluorosilicic acid, sodiumhexafluorosilicate, potassium silicofluoride, aluminium fluoride,flyash, diatomaceous earth, siloxane; and the like. The fluorinecompounds broadly include compounds containing one or more fluorineelements; the tetrafluoroboric acid above is an inorganic acid and alsoa fluorine compound at the same time, and hexafluorosilicic acid, sodiumhexafluorosilicate, and potassium silicofluoride are silicon compoundsas well as fluorine compounds at the same time. Among these reactionretarders, preferable are silicon compounds and fluorine compounds, andmore preferable are noncrystalline silica, white carbon,hexafluorosilicic acid, sodium hexafluorosilicate, potassiumsilicofluoride, aluminium fluoride, and tetrafluorosilicic acid. Thesilicon and fluorine compounds have a dehydration temperature higher andexhibit an effect more favorable than those of other acids even underthe same processing condition, presumably because these compounds areeffective not only in delaying the reaction, but also in acceleratingformation of a glassy layer or a coating layer on the aluminum hydroxidesurface, raising the dehydration temperature because it is necessary tobreak the layer for dehydration by heating. The reaction retarders maybe used in combination of two or more.

The amount of the reaction retarder added to aluminum hydroxide ispreferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts byweight, and still more preferably 0.3 to 3 parts by weight, with respectto 100 parts by weight of aluminum hydroxide. It is because it is notpossible to suppress boehmite conversion of aluminum hydroxidesufficiently at an amount of less than 0.05 parts by weight, and thereaction retarder may remain as an impurity in aluminum hydroxide andreduce the amount of dehydration water relatively, even if harmless asan impurity, at an amount of more than 10 parts by weight. In the fieldof flame retardant, phosphorus- and nitrogen-based and other inorganicflame retardants are often mixed with an aluminum hydroxide flameretardant for synergistic effect, and the reaction retarder may be addedin an amount beyond the range above, if an additive is added for thatpurpose.

The present inventors had filed for a patent of a flame-resistant fillerof boehmite-aluminum hydroxide composite prepared by hydrothermaltreatment of aluminum hydroxide (Japanese Patent Application No.2002-103146). In the invention, increase in boehmite conversion rateresulted in rise of the dehydration temperature of aluminum hydroxidebut drop in the amount of total dehydration water, while decrease inboehmite conversion rate, in drop of the dehydration temperature ofaluminum hydroxide and increase in the amount of dehydration water; andin view of the tradeoff, there existed a problem that it was difficultto raise the dehydration temperature and retain a sufficient amount ofdehydration water at the same time. However, the heat-resistant aluminumhydroxide according to the present invention makes it possible toheighten the dehydration temperature and retain a sufficient amount ofdehydration water by suppressing the boehmite conversion of aluminumhydroxide after a severe heat history, and thus improve both of thecontradicting properties, that is, dehydration temperature and amount ofdehydration water, at the same time. More specifically, when 1%dehydration temperature is defined as a dehydration temperature at whicha flame retardant is dehydrated in an amount of 1%, allowable range inthe amount of dehydration water from a flame retardant in syntheticresin, with respect to the total weight of the flame retardant, incontrast to aluminum hydroxide without hydrothermal treatment having a1% dehydration temperature of about 210 to 230° C., the heat-resistantaluminum hydroxide according to the present invention has a 1%dehydration temperature of 245° C. or more, often 250° C. or more, andstill retain a sufficient amount of dehydration water.

Although the heat-resistant aluminum hydroxide according to the presentinvention include that containing both aluminum hydroxide and boehmiteafter partial boehmite conversion, it preferably has a total amount ofdehydration water of 30% or more, more preferably a boehmite conversionrate of 14% or less and a total amount of dehydration water of 32% ormore, and most preferably a total amount of dehydration water of 35% anda boehmite conversion rate of 0%.

In addition, the heat-resistant aluminium according to the presentinvention preferably has a 1% dehydration temperature of 255° C. or moreand a total amount of dehydration water of 30% or more, and in such acase, the average diameter of the raw aluminum hydroxide is preferably2.5 μm or less.

The heat-resistant aluminum hydroxide according to the presentinvention, which has a high dehydration temperature and a sufficientamount of dehydration water, can be used as a flame retardant in boththermoplastic and thermosetting resins. The heat-resistant aluminumhydroxide may be used in any synthetic resins, whether flammable orflame resistant, and examples of the resins include various syntheticresins such as methyl methacrylic resins, acryl-styrene copolymerresins, ABS resins, polystyrene, polyethylene, polypropylene,polycarbonate, phenol resins, urea resins, melamine resins, epoxyresins, unsaturated polyester, and diallyl phthalate.

The heat-resistant aluminum hydroxide according to the present inventiondescribed above improves the flame-retarding properties of the materialssuch as synthetic resins markedly when it is added.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing thermogravimetric curves of the heat-resistantaluminum hydroxides obtained in Example 7 and Comparative Example 1.

BEST MODE OF CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described with reference toExamples, but it should be understood that the present invention is notrestricted by the following Examples.

Examples 1 to 19

(Preparation of Heat-Resistant Aluminum Hydroxide 1)

A commercially available aluminum hydroxide (manufactured by SumitomoChemical Co., Ltd., hereinafter, C-303) was used in Examples 1 to 11; acommercially available aluminum hydroxide (manufactured by Nippon LightMetal Co., Ltd. hereinafter B703), in Examples 12 and 13; a commerciallyavailable aluminum hydroxide (manufactured by Nippon Light Metal Co.,Ltd. hereinafter, B1403), in Example 14; a commercially availablealuminum hydroxide (manufactured by Nippon Light Metal Co., Ltd.hereinafter, BF013), in Example 15; a commercially available aluminumhydroxide (manufactured by Sumitomo Chemical Co., Ltd., hereinafter,C-3005), in Examples 16 and 17; and a commercially available aluminumhydroxide (manufactured by Showa Denko K.K., hereinafter, H-42M), inExamples 18 and 19, respectively in an amount of 400 g. The reactionretarders used were lactic acid (manufactured by Kanto Chemical Co.Inc.), phosphoric acid (manufactured by Kanto Chemical Co. Inc.),ammonium dihydrogen phosphate (manufactured by Kanto Chemical Co. Inc.),silica (manufactured by Nippon Silica Corp.), a silane-coupling agent(FZ-3794, manufactured by TOSHO Silica Corp.), and white carbon (CarplexCS-5, manufactured by Shionogi & Co., Ltd.), and each reaction retarderwas mixed to aluminum hydroxide in an amount shown in the parenthesis ofTable 1 with respect to 100 parts by weight of aluminum hydroxide. C-303is aluminum hydroxide having an average diameter of 2.5 μm prepared byprecipitation; B 703, aluminum hydroxide having an average diameter 2.0μm prepared by pulverization; B1403, aluminum hydroxide having anaverage diameter of 1 μm prepared by pulverization; BF013, aluminumhydroxide having an average diameter 1.3 μm prepared by precipitation;C-3005, aluminum hydroxide having an average diameter of 0.8 μm preparedby precipitation; and H-42 M, aluminum hydroxide having an averagediameter of 1 μm prepared by precipitation. The reaction conditions,processing temperatures and processing periods are summarized in Table1.

In each Example 3 to 19, the aluminum hydroxide and the reactionretarder shown in Table 1 were blended in a mixer for 30 seconds. Themixture placed in a stainless steel container was treated in anautoclave (electrically heated autoclave equipped with a steamgenerator, manufactured by Osaka Boiler Mfg. Co., Ltd., capacity: 0.4m³) at a predetermined temperature for a particular period. Afterreaction, the resultant reaction product was dried, to give desirableheat-resistant aluminum hydroxide as a colorless powder (dry treatment).Separately, 800 g of aqueous solutions of 1% lactic acid and phosphoricacid were respectively added to and mixed with 400 g of water thoroughlyin Examples 1 and 2 (water ratio (water/aluminum hydroxide by weight):3), and the mixture was subjected to a hydrothermal treatment, to give aheat-resistant aluminum hydroxide as a colorless powder (wet treatment).

Comparative Examples 1 to 10

The aluminum hydroxides of comparative Examples were prepared asfollows: C-303 was used in Comparative Examples 1 to 3; B703, inComparative Example 4; B1403, in Comparative Example 5; BF013, inComparative Example 6; C-3005, in Comparative Examples 7 to 9; and H-42M, in Comparative Example 10, respectively in an amount of 400 g. Thealuminum hydroxides were untreated in Comparative Examples 1, 4, 5, 6,9, and 10. The aluminum hydroxides of Comparative Examples 2, 7, 11, and12 were processed in dry treatment, while those of Comparative Examples3 and 8, in wet treatment.

In Table 1, the raw aluminum hydroxides were grouped according to thekinds into six test groups: C-303 test group, B 703 test group, B1403test group, BF013 test group, C-3005 test group, and H-42 M test group.

[Evaluation of the Properties of Heat-Resistant Aluminum Hydroxide]

Boehmite conversion rate, 1% dehydration temperature (° C.), and thetotal amount of dehydration water (%) of each sample obtained inExamples and Comparative Examples were determined. The boehmiteconversion rate is a percentage of boehmite in the total weight of theproduct obtained by hydrothermal treatment or by applying pressure andheat under steam atmosphere. The boehmite conversion rate was calculatedaccording to the following Formula 1, based on the theoretical totalamounts of dehydration water of pure aluminum hydroxide and boehmite:respectively 34.6% and 15%. The 1% dehydration temperature was atemperature at which an entire sample loses its weight by 1% from theweight of the sample at 100° C. when the sample is heated graduallystarting from 100° C. The total amount of dehydration water was a weightloss from the weight at 100° C. after heating a sample from 100° C. to600° C. The percentage of the total amount of dehydration water is apercentage of the weight of the dehydrated water with respect to theweight of aluminum hydroxide. The 1% dehydration temperature and thetotal amount of dehydration water were determined by thermogravimetricmeasurement using a thermal analyzer (manufactured by Bruker AXS K.K.).The measurement was conducted in atmosphere at programmed heating ratesof 5° C./mim and 10° C./min.34.6X+15Y=ZX+Y=1X=Z−15/19.6  Formula 1(wherein, X: ratio of aluminum hydroxide, Y: ratio of boehmite, and Z:measured amount of dehydration water.)

The boehmite conversion rate (%) is calculated by percentage, bydetermining X by substituting Z with a measured amount of dehydrationwater and subtracting X from 1.

Results are summarized in the following Table 1. The 1% dehydrationtemperatures of the aluminum hydroxides of Examples in the C-303 testgroup were higher by 20 to 38° C. than that of the untreated aluminumhydroxide of Comparative Example 1. In addition, the total amounts ofdehydration water of the aluminum hydroxides of the Examples were almostthe same as that of the untreated aluminum hydroxide of ComparativeExample 1, except in Example 3. The aluminum hydroxide (boehmite) ofComparative Example 2 that was completely converted to boehmite had anextremely low total amount of dehydration water at 15%, although notevaluated because it had a 1% dehydration temperature of around 500° C.The aluminum hydroxide of Comparative Example 3 that was partiallyconverted to boehmite (boehmite conversion rate: 60%) also had a high 1%dehydration temperature similar to those of Examples, but had a totalamount of dehydration water of 23%, which was significantly lower thanthose of the Examples. Namely, as shown in Comparative Example 3, it wasnecessary to raise the boehmite conversion rate to 50% or more forelevating the 1% dehydration temperature of the aluminum hydroxideprepared only from aluminum hydroxide and partially converted toboehmite to a temperature of 260° C., but it is also accompanied withdrastic decrease in the total amount of dehydration water at the sametime.

The 1% dehydration temperatures of the aluminum hydroxides of Examples12 and 13 in the B703 test group were higher by 16° C. than those of theuntreated aluminum hydroxide of Comparative Example 4, but on the otherhand, there was almost no difference in the total amount of dehydrationwater (i.e., Example 13 is the same in dehydrated water quantity asComparative Example 4).

The 1% dehydration temperature of the aluminum hydroxide of Example 14in the B1403 test group was higher by 23° C. than that of the untreatedaluminum hydroxide of Comparative Example 5, and there was no differencein the total amount of dehydration water. The 1% dehydration temperatureof the aluminum hydroxide of Example 15 in the BF013 test group washigher by 28° C. than that of the untreated aluminum hydroxide ofComparative Example 6, and there was no difference in the total amountof dehydration water.

The 1% dehydration temperatures of the aluminum hydroxides of Examples16 and 17 in the C-3005 test group were higher respectively by 34° C.and 37° C. than that of the untreated aluminum hydroxide of ComparativeExample 9, and there was no difference in the total amount ofdehydration water. Further, the 1% dehydration temperatures of thealuminum hydroxides of Examples 16 and 17 were higher by 12 to 23° C.than those of the aluminum hydroxides of Comparative Examples 7 and 8(partially boehmite-converted aluminum hydroxide prepared only fromaluminum hydroxide), and the total amounts of dehydration water of thealuminum hydroxides of these Examples were also higher.

The 1% dehydration temperature of the aluminum hydroxides of Examples 18and 19 in the H-42 M test group were higher respectively by 28° C. and33° C. than that of the untreated aluminum hydroxide of ComparativeExample 10, and there was no difference in the total amount ofdehydration water between the aluminum hydroxides of Example 19 andComparative Example 10.

In Examples 8 to 11, 13, and 17, wherein the boehmite conversion rateswere 0%, the total amounts of dehydration water were 35%, similarly tothose of the untreated aluminum hydroxides of Comparative Examples 1, 4,5, 6, 9, and 10, but the 1% dehydration temperatures of the aluminumhydroxides of the Examples were significantly higher.

In addition, although the boehmite conversion rate of the aluminumhydroxide of Comparative Example 8 in the G-3005 test group was similarto that of Example 19 in the H-42 M test group, the 1% dehydrationtemperature of the heat-resistant aluminum hydroxide of Example 19 wasmarkedly higher than that of Comparative Example 8.

TABLE 1 Total amount of Processing Condition Boehmite 1% Dehydrationdehydration Kind and amount of reaction Temperature conversion ratetemperature (° C.) water Al(OH)₃ retarder (parts by weight) (° C.) Hour(%) (1) (2) (%) Example 1 C-303 test Lactic acid (2) 215 10 5 263 272 34Example 2 group Phosphoric acid (2) 215 10 11 259 268 32 Example 3Ammonium dihydrogen 215 10 34 259 269 28 phosphate (2) Example 4 Silica(0.3) 180 10 3 244 252 34 Example 5 Silica (0.5) 215 5 13 255 265 32Example 6 Silica (1) 215 5 4 254 263 34 Example 7 Silica (1) 215 10 8260 268 33 Example 8 Silica (2) 215 5 0 252 260 35 Example 9 Silica (2)215 10 0 258 268 35 Example 10 Silane-coupling agent (1) 215 3 0 245 25435 Example 11 Silane-coupling agent (1) 215 10 0 258 266 35 ComparativeExample 1 — — — 0 233 234 35 Comparative Example 2 — (Dry treatment) 1705 100 — — 15 Comparative Example 3 — (Wet treatment) 170 6 60 252 263 23Example 12 B703 test Silica (0.5) 215 3 17 252 259 31 Example 13 groupSilica (2) 215 10 0 253 259 35 Comparative Example 4 — — — 0 237 243 35Example 14 B1403 test Silica (1) 215 3 7 241 249 33 Comparative Example5 group — — — 0 217 226 35 Example 15 BF013 test Silica (2) 215 10 5 248255 34 Comparative Example 6 group — — — 0 220 227 35 Example 16 C-3005test Silica (2) 215 10 5 252 260 34 Example 17 group Silane-couplingagent (2) 215 10 0 251 257 35 Comparative Example 7 — (Dry treatment)160 1 15 232 237 32 Comparative Example 8 — (Wet treatment) 170 6 10 241245 33 Comparative Example 9 — — — 0 221 223 35 Example 18 H-42M testSilica (1) 215 10 40 250 257 27 Example 19 group White carbon (2) 215 1010 252 262 33 Comparative Example 10 — — — 0 225 229 35 Examples 1 and2: wet treatment Example 3 to Example 19: dry treatment The 1%dehydration temperatures (1) and (2) were determined respectively underprogrammed heating rates of 5° C./min and 10° C./min.

As apparent from the results above, the heat-resistant aluminumhydroxides in Examples are new aluminum hydroxides having a controlledboehmite conversion rate and a markedly heightened dehydrationtemperature and retaining a sufficient amount of dehydration water evenafter a severe heat history (high processing temperature and longprocessing period). There was no significant difference due todifference of the raw aluminum hydroxide used among the test groups, andthe 1% dehydration temperatures in Examples were significantly higherthan those in Comparative Examples in each test group and theheat-resistant aluminum hydroxides in Examples retained a sufficientamount of dehydration water.

Examples 20 to 40

(Preparation of Heat-Resistant Aluminum Hydroxide 2)

Heat-resistant aluminum hydroxides were prepared under a predeterminedcondition by using the reaction retarders shown in Table 2. C-303 wasused as the raw aluminum hydroxide in Examples 20 to 39, and BF083(manufactured by Nippon Light Metal Co., Ltd. average diameter: 8 μm) inExample 40. The heat-resistant aluminum hydroxides of Examples exceptthose of Examples 25, 26, 36, and 37 were prepared in a similar mannerto Examples 3 to 19 above (preparation of heat-resistant aluminiumhydroxides 1) (dry treatment). The heat-resistant aluminum hydroxide ofExample 25 was prepared by mixing 1 g of white carbon to 50 g ofaluminum hydroxide in a mixer and processing the mixture in an autoclave(externally heated autoclave, manufactured by Osaka Boiler Mfg. Co.,Ltd., capacity: 100 ml, withstanding pressure: 5 MPa). Theheat-resistant aluminum hydroxide of Example 26 was prepared by mixing10 kg of white carbon to 500 kg of aluminum hydroxide in a mixer andprocessing the mixture in an autoclave (steam-supplying autoclave,manufactured by Osaka Boiler Mfg. Co., Ltd., capacity: 3.6 m³,withstanding pressure: 3 MPa). The heat-resistant aluminum hydroxide ofExample 36 was prepared by placing 2 g (2 parts by weight) of whitecarbon and 100 g (100 parts by weight) of aluminum hydroxide in anautoclave (externally heated autoclave, manufactured by Osaka BoilerMfg. Co., Ltd., capacity: 5 L, withstanding pressure: 3 MPa) and heatingthe mixture at 200° C. for 5 hours without addition of additional wateror steam (i.e., under an unsaturated steam condition). The maximumpressure during heating was 250 kPa. The heat-resistant aluminumhydroxide of Example 37 was prepared by placing 12 g (2 parts by weight)of white carbon and 600 g (100 parts by weight) of aluminum hydroxide inan autoclave (externally heated autoclave, manufactured by Osaka BoilerMfg. Co., Ltd., capacity: 5 L, withstanding pressure: 3 MPa), applying apressure of 700 kPa from outside with a compressed air at normaltemperature (20° C.) and heating the mixture at 200° C. for 12 hourswithout addition of additional water or steam (i.e., under anunsaturated steam condition). The white carbon used was Nipsil LP(manufactured by Toso Silica Corporation).

Comparative Examples 11 to 13

The aluminum hydroxides (boehmite) of Comparative Examples 11 and 12were prepared in a similar manner to Examples 3 to 19 above (preparationof heat-resistant aluminium 1) by using C-303 as the raw aluminumhydroxide (dry treatment). In Comparative Example 13, the raw aluminumhydroxide used was BF083.

The boehmite conversion rates, the 1% dehydration temperatures (° C.),and the total amounts of dehydration water (%) of the aluminumhydroxides of the Examples 20 to 38 and Comparative Examples 11 to 13were determined in a similar manner to (preparation of heat-resistantaluminum hydroxides 1). Results are summarized in Table 2.

TABLE 2 Processing condition Boehmite 1% Dehydration Total amount ofKind and amount of reaction Temperature conversion rate temperature (%)dehydration Al(OH)₃ retarder (parts by weight) (° C.) Hour (%) (1) (2)water (%) Comparative C-303 test Silica (0.01) (dry treatment) 180 5 100— — 15 Example 11 group Comparative Silica (0.03) (dry treatment) 180 5100 — — 15 Example 12 Example 20 Silica (0.05) 180 5 20 248 255 31Example 21 Sodium hexafluorosilicate (2) 210 12 5 266 273 34 Example 22Potassium silicofluoride (2) 210 12 7 263 270 33 Example 23Hexafluorosilicic acid (2) 210 12 4 270 279 34 Example 24Tetrafluoroboric acid (2) 210 12 3 269 279 34 Example 25 White carbon(2) 250 12 16 264 273 31 Example 26 White carbon (2) 228 12 9 — 272 33Example 27 Sodium dihydrogen bisphosphate 1 210 12 10 262 271 33 hydrate(2) Example 28 Fumaric acid (2) 210 12 6 263 — 33 Example 29 Sodiumdihydrogen phosphate (2) 210 12 10 253 — 33 Example 30 Tartaric acid (2)210 12 4 260 — 34 Example 31 Diatomaceous earth (2) 210 12 6 258 — 33Example 32 Sodium metaphosphate (2) 210 12 13 254 — 32 Example 33 Flyash(2) 210 12 10 254 — 33 Example 34 Sodium hexametaphosphate (2) 210 12 5253 — 34 Example 35 Siloxane (1) 210 12 5 260 — 34 Example 36 Whitecarbon (2) 200 5 3 — 273 33 Example 37 White carbon (2) 200 12 8 — 27133 Example 38 Aluminium fluoride (2) 210 12 5 — 280 34 Example 39Aluminium fluoride (2) + 210 12 0 — 280 35 white carbon (2) Example 40BF083 test White carbon (2) 210 12 23 265 — 30 Comparative group — — — 8231 — 33 Example 13 The 1% dehydration temperatures (1) and (2) weredetermined respectively under programmed heating rates of 5° C./min and10° C./min.

As apparent from Table 2, the heat-resistant aluminum hydroxides ofExamples 20 to 40 had a high 1% dehydration temperature and a high totalamount of dehydration water. The aluminum hydroxides (boehmite) ofComparative Examples 11 and 12 had a total amount of dehydration waterof less than half of those of Examples because of complete conversion toboehmite due to the low content of the added reaction retarder silica.Alternatively, the aluminum hydroxide of Comparative Example 13 had ahigh total amount of dehydration water but a lower dehydrationtemperature.

Because dehydration in an amount of 0.5% or more is not allowed when theheat-resistant aluminum hydroxide according to the present invention isadded to a printed wiring substrate, the 0.5% dehydration temperaturesof the aluminum hydroxides of the Examples and the Comparative Examplesshown in Tables 1 and 2 were also determined and are summarized in Table3. The 0.5% dehydration temperature is a dehydration temperature atwhich the water in aluminum hydroxide was dehydrated in an amount of0.5% with respect to the total weight.

As apparent from Table 3, the heat-resistant aluminum hydroxides ofExamples had a dehydration temperature higher than that of ComparativeExamples even at the 0.5% dehydration temperature. The thermogravimetriccurves of the aluminum hydroxides of Example 7 and Comparative Example 1in Table 3 were shown in FIG. 1. As apparent, there are distinctdifferences both in 0.5% and 1% dehydration temperature between thesealuminum hydroxides.

TABLE 3 Processing condition Boehmite 1% Dehydration Total amount ofKind and amount of reaction Temperature conversion temperature (° C.)dehydration Al(OH)₃ retarder (parts by weight) (° C.) Hour rate (%) 0.5%1% water (%) Comparative C-303 test — — — 0 225 233 35 Example 11 groupExample 7 Silica (1) 215 10 8 253 260 33 Example 22 Sodiumsilicofluoride (2) 210 12 7 249 263 33 Example 23 Hexafluorosilicic acid(2) 210 12 4 260 270 34 Example 25 White carbon (2) 250 12 16 258 264 31Example 30 Tartaric acid (2) 210 12 4 249 260 34 Example 31 Diatomaceousearth (2) 210 12 6 250 258 33 Example 32 Potassium metaphosphate (2) 21012 13 254 254 32 Example 35 Siloxane (1) 250 12 5 251 260 34 Example 38BF083 test White carbon (2) 210 12 23 258 265 30 Comparative group — — —8 225 231 33 Example 13[Test on Foaming During Polypropylene Molding 1]

The heat-resistant aluminum hydroxide of Example 9 was kneaded as aflame retardant in polypropylene (PP) under the following condition, andpresence of foams in the resin extruded from a die was determined byvisual observation. Separately, foaming of the PP resin containing acommercially available aluminum hydroxide (untreated) kneaded wasevaluated in a similar manner for comparison.

PP used: melt index (MI): 1

Resin kneader: biaxial extruder, manufactured by Ikegai Ltd. PCM45(diameter: 45 mm),

Cylinder temperature: 200 to 230° C. (set temperature)

Die temperature: 220 to 230° C. (set temperature), 240 to 250° C.(measured value),

Rotational frequency: 100 rpm

Flame retardant added: 100 parts with respect to 100 parts by weight ofPP (also in Comparative Example)

The results of the tests above revealed that there was no foamingobserved in the flame retardant of Example 9 but there was some foamingin that of Comparative Example.

[Test on Foaming During Polypropylene Molding 2]

Compounds were prepared by supplying each of the aluminum hydroxidesprepared in the Examples and Comparative Examples shown in Tables 1 and2 in an amount of 100 parts by weight with respect to 100 parts byweight of raw polypropylene (PP) from an automatic measuring hopper byusing a biaxial extruder (KZW15TW-45MG-NH(−700), manufactured byTechnovel Corporation).

The feeding rate of the entire raw materials was 2 kg/hr; the mixturewas melt-blended at a predetermined temperature and extruded into astrand (linear resin compound) of 2 mm in diameter; and foaming of thestrand was evaluated. Foamed strands had air bubbles inside and surfaceirregularity, and thus, presence of foams was evaluated by theappearance (without foaming: ◯, with foaming: x).

Results are summarized in Table 4.

Basic Extruding Condition

Screw rotational frequency: 350 rpm

Molding Zone Temperature:

(Condition 1) from entrance side: 100-200-200-200-200-200° C.

(Condition 2) from entrance side: 100-200-220-220-220-220° C.

(Condition 3) from entrance side: 100-200-230-230-230-230° C.

Die Temperature;

(Condition 1) 200° C.

(Condition 2) 220° C.

(Condition 3) 230° C.

TABLE 4 Foaming test Condition 1 Condition 2 Condition 3 Example 1 ∘ ∘Example 2 ∘ ∘ ∘ Example 7 ∘ ∘ ∘ Example 8 ∘ ∘ ∘ Example 9 ∘ ∘ ∘Comparative ∘ x x Example 1 Example 13 ∘ ∘ ∘ Comparative ∘ x x Example 4Example 14 ∘ ∘ x Comparative x x x Example 5 Example 15 ∘ ∘ xComparative x x x Example 6 Example 16 ∘ ∘ x Comparative x x x Example 9Example 18 ∘ ∘ x Comparative x x x Example 10 Example 21 ∘ ∘ ∘ Example23 ∘ ∘ ∘

As apparent from Table 4, foaming of all aluminum hydroxides ofComparative Examples was observed at a lower temperature, while nofoaming of the aluminum hydroxides of Examples was observed even at ahigher molding temperature, improving the yield of products even at arelatively higher temperature. In examples, aluminum hydroxides having agreater average particle diameter were superior in heat resistance.

[Test of Foaming of Epoxy Resin Film 1]

Each of the aluminum hydroxides of Example 8 and Comparative Examples 1and 3 shown in Table 1 was added in an amount of 100 parts by weight to100 parts by weight of an epoxy resin, and the mixture was cast into afilm and cured in a dryer at 200° C. The film thus obtained was placedin a dryer at 280° C., and the period until foaming was determined. Asshown in Table 5, the film containing the aluminum hydroxide of Example8 had a period until foaming markedly longer and a heat resistancehigher than those of the films respectively containing the aluminumhydroxide of Comparative Example 1 and 3.

TABLE 5 Heat resistance of epoxy resin film at 280° C. Example 8 25 minComparative Example 1 <1 min Comparative Example 3 10 min[Test of Foaming of Epoxy Resin Film 2]

Each of the aluminum hydroxides of Example 8 and Comparative Example 1shown in Table 1 was added in an amount of 100 parts by weight to 100parts by weight of an epoxy resin, and the mixture was cast into a filmand cured in a dryer at 200° C. Foaming of each of the epoxy resin filmscontaining aluminum hydroxide was determined after treatment in a reflowfurnace under the following conditions. As shown in Table 6, the filmcontaining the aluminum hydroxide of Example 8 showed no foaming, whilethat of Comparative Example 1 showed foaming.

Reflow Conditions

Reflow furnace length: 4 m

Traveling speed: 0.8 m/min

Preheater: 150° C.

Reflow temperature: 250° C.

Reflow period: 40 seconds

TABLE 6 Heat resistance of epoxy resin film in reflow furnace Example 8Comparative Example 1 x

INDUSTRIAL APPLICABILITY

The heat-resistant aluminum hydroxide according to the presentinvention, which has a dehydration temperature higher than that ofpreexisting aluminum hydroxides and still has a sufficiently great totalamount of dehydration water, is extremely useful as a flame retardant,avoids reliably the foaming in synthetic resin molded products due todehydration of flame retardant at an environment temperature of moldingand using the synthetic resins, improves productivity without loweringthe yield of synthetic resin molded products, allows cost reduction, andexerts an excellent flame-retarding effect.

By using the properties of the heat-resistant aluminum hydroxideaccording to the present invention having a dehydration temperaturehigher than that of preexisting aluminum hydroxides and still having asufficiently large total amount of dehydration water, it would also bepossible to use the aluminum hydroxide in applications other than flameretardants.

In addition, the method of producing the heat-resistant aluminumhydroxide according to the present invention provides the aluminumhydroxide having a higher dehydration temperature and a sufficient largetotal amount of dehydration water that is extremely useful as a flameretardant. The method of producing the heat-resistant aluminum hydroxideaccording to the present invention by heating a raw mixture of aluminumhydroxide and a reaction retarder for delaying the boehmite conversionin a pressure vessel without addition of water eliminates the need fordrying the heat-resistant aluminum hydroxide, reduces the pressureduring production to the saturated steam pressure or less, and thus,allows production thereof in a pressure vessel designed to have a lowwithstanding pressure and reduction in facility investment andproduction cost.

What is claimed is:
 1. A heat-resistant aluminum hydroxide produced by ahydrothermal treatment of a raw material mixture of aluminum hydroxideand at least a boehmite conversion reaction retarder selected from thegroup consisting of lactic acid, phosphoric acid, silica,silane-coupling agent, white carbon, sodium dihydrogen bisphosphate 1hydrate, fumaric acid, sodium dihydrogen phosphate, tartaric acid,diatomaceous earth, sodium metaphosphate, sodium hexametaphosphate, andsiloxane under a processing temperature at 170° C. or more and 250° C.or less, and said heat-resistant aluminum hydroxide has a boehmite andwhere said boehmite is 14% or less of the total weight of the productobtained by said hydrothermal treatment.
 2. The heat-resistant aluminumhydroxide according to claim 1, wherein the amount of the reactionretarder added is 0.05 to 10 parts by weight with respect to 100 partsby weight of the aluminum hydroxide.
 3. A heat-resistant aluminumhydroxide, wherein said hydroxide has a 1% dehydration temperature of255° C. or more and a total amount of dehydration water of 30% or more.4. The heat-resistant aluminum hydroxide according to claim 3, whereinthe average diameter of the aluminum hydroxide is 2.5 μm or less.
 5. Aflame retardant, wherein said retardant includes the heat-resistantaluminum hydroxide according to any one of claims 1, 2, 3 or
 4. 6. Asynthetic resin composition, wherein said composition contains the flameretardant according to claim
 5. 7. The synthetic resin compositionaccording to claim 6, wherein the synthetic resin is polypropylene. 8.The synthetic resin composition according to claim 6, wherein thecomposition is a printed wiring board.
 9. A method of producing aheat-resistant aluminum hydroxide, further comprising processing a rawmixture of aluminum hydroxide and at least a boehmite conversionreaction retarder selected from the group consisting of lactic acid,phosphoric acid, silica, silane-coupling agent, white carbon, sodiumdihydrogen bisphosphate 1 hydrate, fumaric acid, sodium dihydrogenphosphate, tartaric acid, diatomaceous earth, sodium metaphosphate,sodium hexametaphosphate, and siloxane by hydrothermal treatment under aprocessing temperature at 170° C. or more and 250° C. or less and saidheat-resistant aluminum hydroxide has a boehmite and where said boehmiteis 14% or less of the total weight of the product obtained by saidhydrothermal treatment.
 10. The method of producing a heat-resistantaluminum hydroxide according to claim 9, wherein the amount of thereaction retarder added is 0.05 to 10 parts by weight with respect to100 parts by weight of aluminum hydroxide.